1. Field of the Invention
The invention relates to a device by tubing in an oil well or a gas well, hereinafter only referred to as a well.
2. Description of the Related Art
In the production of oil and gas, oil/gas is led to the surface through so-called tubing in a well. At the surface, at the upper end of the tubing, comprehensive valving and safety equipment are arranged thereto. Somewhat away from its lower end, the tubing has a seal arranged thereto, the so-called packer, which is arranged to seal between the tubing and the wall of the well, which is normally lined with a steel tube also called casing, so that oil or gas cannot enter the annulus outside the tubing. Between said packer and the lower end of the well, the casing is perforated, so that oil or gas may flow into the well, further up into the tubing and to the surface. In the annulus outside the casing and between the packer and the lower end of the casing, a filter, for example a gravel pack, may be provided, which is to prevent sand from the reservoir from being carried by the gas or oil flow.
The lower end of the casing which is in the productive zone of the well, i.e. the part of the casing located between the packer and the bottom of the well, is of particular interest and calls for attention for several reasons. It is desirable to be able to decide which part of the reservoir to produce from. This is decided partly by positioning the perforations in the right area of the casing. It is typical to carry out perforation in several turns to exploit the reservoir, zone by zone, in the course of time. There may also be drilled extensions from the lower part of the casing out into the reservoir. It is further known to install zone defining packers in the annulus between the casing and the wall of the well. By installing plugs and chokes, maybe choke valves, within the lower part of the casing, the production from the reservoir may be controlled, so that the reservoir is drained in the optimal manner.
To monitor the production and ensure optimal conditions, it is known to arrange downhole sensors to observe pressure, temperature, water content in the oil/gas, detect sand and other items. The sensors should be placed in the productive part of the well, i.e. between the packer and the bottom of the well.
Sensor signals are transferred to the surface through lines running in the annulus outside the tubing. The sensors are installed at the same time as the tubing, and the lines are secured to the exterior of the tubing. Possible actuators for downhole valves are energized by lines from the surface and are controlled from the surface, either by controlling the energy supply or through particular control signals. Both electric and hydraulic lines may be of interest.
Deposits occur in the tubing, particularly in the lower part of the tubing. In connection with well maintenance it is of current interest to perform mechanical cleaning inside the tubing. Sensors, actuators, chokes and other equipment must either be arranged to bear and give room for such cleaning, or the equipment must be removed before cleaning is started.
The packer is of great importance in terms of safety, and quite naturally there are strict requirements to the packer itself and to the setting of it. The packer may not be removed, unless other satisfactory security is provided.
When equipment, to be connected to lines from the surface, is placed closer to the well bottom than the packer, problems arise in passing the lines past the packer. The lines may be taken through the packer itself, but this requires particular measure. The lines may be taken through the tubing wall further away from the end of the tubing than where the packer is, and back out, nearer the end of the tubing. The lines will then run inside the tubing a short distance, and will then be highly exposed. Therefore, it is a better solution to pass the lines past the packer in channels in the tube wall itself. Still, a sealing problem will arise, as oil and gas may then enter the annulus between the packer and the surface. Sensors and other equipment, to be connected to lines and placed closer to the well bottom than the packer, must be installed at the same time as the tubing. Maintenance of such equipment often involves that the tubing must be extracted from the well, which is, of course, both complex and expensive.
A superior object of the invention is, therefore, to simplify the maintenance and use of equipment in an area between the packer and the well bottom. In particular it is an object to simplify installation and maintenance of equipment which is to be connected to lines in said area.